Every time I hear the word, I think of these guys:
We were tweens before it was cool!
Merry and Pippin are the archetypal tweens in my mind: fun-loving young people who don't take life too seriously and offer some much-needed comic relief.
Pippin: Anyways, you need people of intelligence on this sort of... mission... quest... thing.
Merry: Well, that rules you out, Pip.
And they're always thinking about food.
Pippin: What about breakfast?
Aragorn: You've already had it.
Pippin: We've had one, yes. What about second breakfast?
[Aragorn turns and walks off in disgust]
Merry: I don't think he knows about second breakfast, Pip.
Pippin: What about elevenses? Luncheon? Afternoon tea? Dinner? Supper? He knows about them, doesn't he?
Merry: I wouldn't count on it.
I for one am going to continue using tween to refer to people like Merry and Pippin. What about you? What do you think?